The Geometry.jsm JavaScript code module provides routines for performing common geometry operations on points and rectangles. It exports two classes: Point and Rect.
To use these routines, you first need to import the code module into your JavaScript scope:
Components.utils.import("resource://gre/modules/Geometry.jsm");
Once you've imported the module, you can then use the Point and Rect classes.
Note: Although this module is usable from mobile, and is present in Firefox 4, it's currently not used in Firefox 4 and attempting to use it may produce unreliable results there.